This invention relates to a method and apparatus for producing bag making material, and is more particularily concerned with producing such material from laminated film which is equipped with extruded complementary separable fastener profile strips.
Bag making material of this general type may be produced in apparatus as disclosed in U.S. Pat. No. 3,787,269, but which has certain limitations that are overcome by the present invention. To any extent necessary for better understanding of the present invention, the disclosure of this patent is included herein by reference.
As pointed out in that patent, conventional reclosable plastic bags featuring various types of plastic fasteners have consisted of a simple combination of fastener means and bag bodies, both of which are formed integrally and at the same time, often monolithically extruded, of a single plastic or resin material, such as, polyethelyene or polypropylene. Since such extrusion forms a single sheet that is not absolutely airtight, bags made therefrom are inadequate for medicines or foods, the quality of which might be affected by intrusion of air or moisture. To alleviate that problem, the bag bodies have been formed of more air impervious laminated films, which may be formed from cellophane, and/or paper, and/or aluminum, etc., and with a resin coating such as polyethelyene or other plastic. However, production of such laminated films or sheets and fastener means by extruding both the film and the fastener means at the same time is virtually impossible. Further, considering the matter in reverse, a method of laminating another different film or substrate on a monolithically formed fastener carrying extruded film is not desirable, because in the attachment process the pressure that may be added for attaching the sheet elements together, generally requiring heating and pressure, may cause changes in the structural form of the fastener means.
There is more disclosure in the aforesaid patent relating to particular treatment by way of heating and controlled coolant to avoid wrinkling and the like, and which in view of the patent disclosure may be only superficially alluded to herein. Solution of a different problem is addressed herein.
That problem arises because in the machine of the patent disclosure there has been a limitation on the type of bag material that may be produced. That is, the patent disclosure teaches only the production of open bottom bag material, wherein the separable fastener profiles strips are attached in such a manner at the longitudinal central portion of the sheet that by folding the sheet upon itself the fasteners will be brought together at a closed top of the bag, while the bottom of the bag will be left open for filling from the bottom and the bottom opening then sealed.
On the other hand, efficient bag filling machines have been developed for filling separable fastener equipped bags from the top by separating, or maintaining separated, the separable fastener elements and then forcing the fastener elements into bag closing cooperation. It is to the production of open top, close bottom, top fillable bag material that the present invention is directed, while utilizing other desirable attributes of the machine disclosed in the aforesaid patent.
Just by way of further background, certain other prior art patents may be referred to as follows:
U.S. Pat. No. Re. 28,959 discloses the monolithic, tubular extrusion of bag making film and fastener profiles for the production of open top bags.
U.S. Pat. No. 4,101,355 discloses applying freshly extruded fastener strips to freshly extruded film, or attachment of preformed fastener strips to preformed film by adhesive means, but wherein all of the attachment or joinder of components is effected while the film or sheet is travelling in a flat state.
U.S. Pat. No. 4,259,133 discloses concurrent extrusion of film and fastener profile strips which are immediately fused together to, in effect, produce a monolithic structure for either open bottom or open top bag making material.
U.S. Pat. No. 4,341,575 discloses applying prefabricated fastener strip to prefabricated film by means of adhesive bonding, for producing either open top or open bottom bag material. There is no indication of applying freshly extruded fastener strip to preformed film in this patent disclosure.
In none of the foregoing patent disclosures is there any suggestion to be derived for producing open top, closed bottom bag material by simple, efficient modification of apparatus according to the disclosure in aforesaid U.S. Pat. No. 3,787,269. In particular those prior patents do not teach how to join fastener strips, extruded from adjacently spaced extrusion orifices, to the opposite side portions of travelling continuous web, film or sheet, so that the profiles of the strips will join for separably closing open top bags when the sheet is folded on itself and the fold provides for closed bottoms for the bags.